Interactive input systems that allow users to inject input (i.e. digital ink, mouse events etc.) into an application program using an active pointer (e.g. a pointer that emits light, sound or other signal), a passive pointer (e.g. a finger, cylinder or other suitable object) or other suitable input device such as for example, a mouse or trackball, are known. These interactive input systems include but are not limited to: touch systems comprising touch panels employing analog resistive or machine vision technology to register pointer input such as those disclosed in U.S. Pat. Nos. 5,448,263; 6,141,000; 6,337,681; 6,747,636; 6,803,906; 7,232,986; 7,236,162; and 7,274,356 assigned to SMART Technologies ULC of Calgary, Alberta, Canada, assignee of the subject application, the entire contents of which are incorporated herein by reference; touch systems comprising touch panels employing electromagnetic, capacitive, acoustic or other technologies to register pointer input; laptop and tablet personal computers (PCs); personal digital assistants (PDAs) and other handheld devices; and other similar devices.
Above-incorporated U.S. Pat. No. 6,803,906 to Morrison et al. discloses a touch system that employs machine vision to detect pointer interaction with a touch surface on which a computer-generated image is presented. A rectangular bezel or frame surrounds the touch surface and supports digital cameras at its corners. The digital cameras have overlapping fields of view that encompass and look generally across the touch surface. The digital cameras acquire images from different vantages and generate image data. Image data acquired by the digital cameras is processed by on-board digital signal processors to determine if a pointer exists in the captured image data. When it is determined that a pointer exists in the captured image data, the digital signal processors convey pointer characteristic data to a master controller, which in turn processes the pointer characteristic data to determine the location of the pointer in (x, y) coordinates relative to the touch surface using triangulation. The pointer coordinates are conveyed to a computer executing one or more application programs. The computer uses the pointer location data to update the computer-generated image that is presented on the touch surface. Pointer contacts on the touch surface can therefore be recorded as writing or drawing or used to control execution of an application program executed by the computer.
In interactive input systems that employ machine vision technology to register pointer input, when only a single pointer exists in captured image frames, the location of the pointer in (x, y) coordinates relative to the touch surface can be readily computed using triangulation. However, when multiple pointers exist in captured image frames, computing the positions of the pointers in (x, y) coordinates relative to the touch surface is more complicated as pointer ambiguity and/or pointer occlusion conditions may exist. For example, when multiple pointers are contacting the input surfaces, there are positions where one pointer may partially or completely obscure another pointer from the view of an imaging device, giving rise to ambiguity as to the location of the pointers.
Several approaches for improving detection of multiple pointers in interactive input systems have been considered. For example, U.S. Patent Application Publication No. 2008/0143690 to Jang et al. discloses a display device comprising a plurality of cameras positioned at the corners of a touch surface. Each camera takes images of the touch surface, on which multiple touch locations are present. The image data are then sent to a signal processor of a control board. The signal processor detects the touch locations from the image data of the cameras and the angle of each touch location with respect to each camera and finds the coordinate of each touch location. During the calculation, the angle measured, which has been distorted by the lens of the camera is compensated by a look-up-table stored in the control board. Therefore, each location of multi-touch can be accurately detected.
U.S. Patent Application Publication No. 2007/0116333 to Dempski et al. discloses a system and method for determining positions of multiple targets on a touch surface. At least two cameras are positioned at the corners of the touch surface to acquire images of the multiple simultaneous targets on the touch surface. The information from the cameras is used to generate possible targets. The possible targets include both “real” targets (a target associated with an actual touch) and “ghost” targets (a target not associated with an actual touch). Using an analysis of tracking a history of previous targets, such as finding the distance and direction of a present target relative to its associated previous target, the real targets are found and the ghost targets are deleted from the list of the potential targets.
U.S. Patent Application Publication No. 2008/0291164 to Tanaka discloses a coordinate input apparatus for detecting multiple inputs. A plurality of sensor units for receiving arrival light detects the light-shielding ranges caused by pointers present on the coordinate input apparatus. The information of each end of the light-shielding ranges, such as the coordinate and the angle are calculated on the basis of the number of the ranges in the respective sensor units. An input transient state in which two light-shielding ranges are partially or totally overlapped is detected. True coordinative values of the pointers are finally determined based on a selection of a coordinate-calculation first data and a coordinate-calculation second data, which is angle information of the ends of the light-shielding ranges.
U.S. Patent Application Publication No. 2010/0201812 to McGibney et al. entitled “Active Display Feedback in Interactive Input Systems” filed on Feb. 11, 2009 and assigned to SMART Technologies, ULC, discloses a method for distinguishing a plurality of pointers in an interactive input system and an interactive input system employing the method. During the method, a plurality of potential coordinates for a plurality of pointers in proximity of an input surface is calculated. Visual indicators associated with each potential coordinate on the input surface are displayed and real pointer locations and imaginary pointer locations associated with each potential coordinate are determined from the visual indicators.
U.S. Patent Application Publication No. 2011/0006981 to Chtchetinine et al. entitled “Interactive Input System” filed on Jul. 10, 2009 and assigned to SMART Technologies, ULC, discloses an interactive input system and method for resolving ambiguities between at least two pointers in a plurality of input regions defining an input area. The method comprises capturing images of the plurality of input regions, the images captured by plurality of imaging devices each having a field of view of at least a portion of the input area, processing image data from the images to identify a plurality of targets for the at least two pointers within the input area and analyzing the plurality of targets to resolve a real location associated with each pointer.
Although the above-mentioned interactive input systems allow multiple pointer contacts to be determined, alternative methods to resolve multiple pointer contacts are desired. It is therefore an object of the present invention to provide a novel interactive input system and method.